1. Field of the Invention
This patent specification relates to transducer assemblies for use in downhole tools. More particularly, this patent specification relates to sealed acoustic transducer assemblies for use in logging while drilling applications downhole.
2. Background of the Invention
In the oil and gas industry, subsurface formations are typically probed by well logging instruments to determine the formation characteristics. For example sonic tools have been found to provide valuable information regarding subsurface acoustic properties, which may be used to produce images or derive related characteristics for the formations.
For example conventional acoustic tools are equipped with acoustic transducer elements, such as piezoelectric elements. In general such transducer elements have to be isolated from external fluid in downhole environment. However, the transducer elements have difficulty making proper measurements when the pressure of the external fluid is changing, as often is the case in the downhole environment.
Conventional designs of housings for acoustic transducers for use in while drilling applications include sealing the transducer from the external environment using molded rubber that surrounds the transducer. For example, U.S. Pat. No. 7,364,007, which is incorporated herein by reference, discusses transducers and associated electronics modules that are packaged and sealed for exposure to harsh environments, without oil compensation. The sealing material, such as molded rubber, encases the transducer and electronics. Similarly, U.S. Pat. No. 7,460,435, which is incorporated herein by reference, discusses acoustic sources for downhole use that are encased in a liquid-free sealing material, such as molded rubber, for protection.
However, there are number of problems associated with encasing the acoustic transducers and electronics in molded rubber. For example, in some cases it may be difficult to repair a transducer assembly that has suffered an internal component failure. Another potential problem is that manufacturing issues can arise due to high temperatures and/or pressures that may be part of the manufacturing process. Another potential problem is that when positioned downhole, in certain situations there can be problems associated with gas absorbing or otherwise being trapped in the transducer assembly.
Thus, there is a need of transducer assemblies that alleviate some or all of the foregoing problems with conventional designs for downhole transducer assemblies.